Filtern
Dokumenttyp
- Zeitschriftenartikel (9) (entfernen)
Schlagworte
- Gefüge (2)
- A. Stainless steel (1)
- Automobilbau (1)
- Automobilindustrie (1)
- Automotive engineering (1)
- B. SEM (1)
- Berlin Freedom Bell (1)
- Betriebsfestigkeit (1)
- C. Corrosion fatigue (1)
- C. Kinetic parameters (1)
In einem Gemeinschaftsprojekt der Stahl- und Automobilindustrie wurden an zwanzig Stählen für Feinblech elastische, plastische und zyklische Kennwerte für die FE-Simulation ermittelt. Die Untersuchungen mit dem Ziel, Eingabekennwerte für FE-Berechnungen zu erhalten, erbrachten einen erheblichen Erfahrungszuwachs im Bereich der Messtechnik sowie der Datenerfassung und -weiterverarbeitung. Der vorliegende Beitrag gibt einen Überblick über die Untersuchung und ihre Ergebnisse.
This paper deals with life prediction by observation and simulation of short fatigue cracks in cyclically loaded smooth and notched specimens made of 0.15 wt-% carbon steel SAE1017. The measured crack behaviour was simulated in a microstructural environment. Reference tests under constant amplitude loading allowed to determine model parameters and hence a reasonable life prediction by simulation resulted even for service loading. Short crack behaviour was a measurable property for damage also to compare smooth and notched specimens.
Im Rahmen eines gemeinschaftlichen Projektes der Stahl- und Automobilindustrie wurden für 17 Stahlfeinbleche des Automobilbaus in verschiedenen Anlieferungs- und Verformungszuständen unter -40°C, Raumtemperatur und +100°C mit 37 Versuchsreihen Anrisswöhlerlinien und zügige bzw. zyklische Spannung-Dehnung-Kurven bestimmt. Sämtliche Versuchspunkte, Hysteresen und ermittelte zyklische Kennwerte liegen in einer Datenbank vor. Eine Korrelationen zwischen den Kennwerten aus dem Zugversuch und den Kennwerten aus den zyklischen, dehnungsgeregelten Versuchen ist grundsätzlich möglich.
Die Verwendung von höherfesten, vergüteten Stählen für Radsatzwellen wird zurzeit kontrovers diskutiert. Für die zuverlässige Auslegung mit diesen Werkstoffen werden verlässliche mechanische und bruchmechanische Kennwerte benötigt. Zudem müssen die aus Prüfungen an Kleinproben und Bauteilen gewonnenen Werte konsistent sein. Das war bisher nicht immer der Fall.
In einem von der Bundesanstalt für Materialforschung und -prüfung (BAM) Berlin im Auftrag des Verbandes der Bahnindustrie in Deutschland (VDB) durchgeführten Forschungsvor- haben wurden Proben aus dem Werkstoff A5T (42CrMo4+QT), entnommen aus Original-Radsatzwellen und aus 1:1-Proben eines anderen Forschungsvorhabens, untersucht. Alle Proben haben für den Werkstoff A5T und seinem Wärmebehandlungszustand den gültigen Normen entsprechende Kennwerte im Rahmen der geforderten Eigenschaften gezeigt. Gefügefehler konnten an den vorliegenden Prüfstücken nicht nachgewiesen werden. Die vorgenommenen Wärmebehandlungen beeinflussen das Gefüge und die mechanischen Eigenschaften in der erwarteten Weise.
On October 24th 1950 the 'Freedom Bell' rung for the first time in the tower of the former West Berlin town hall. One year after the Berlin blockade and at a first climax of the 'Cold War', the 'American National Committee for a Free Europe' donated the bell to the city of West Berlin. The bronze bell has a weight of about 10 tons. Its clapper has a length of 2.40 m and a weight of nearly 1 ton. In 1966 the hanging of the clapper and in 1979 the clapper of the bell broke down. Both failures were found to be caused by fatigue fracture. In 1974, a crack in the bell body was detected. After years of periodic monitoring using non-destructive testing, the crack was closed in 2001.
In corrosive environments such as CCS bore holes or geothermal power plants the materials loaded cyclically are also exposed constantly to the highly corrosive hot thermal water. The lifetime reduction of (X46Cr13, AISI 420C) is demonstrated in in-situ-laboratory experiments (T=60 °C, geothermal brine: Stuttgart Aquifer flow rate: 9 Nl/h, CO2). S-N plots, micrographic-, phase-, fractographic- and surface analysis were applied to obtain sustainable information on the corrosion fatigue behavior. Maximum number of cycles (here 12.5 x 106 cycles to failure) is reached at σa =173 MPa. No typical fatigue strength exists and passive corrosion fatigue is most likely failure cause.
In July 1968 the Swedish motor vessel 'MV Stureholm' traveled from Sweden across the North Atlantic with destination to the American gulf harbours. MV Stureholm was a freighter with 9700 tdw build in 1957 by a German shipyard. About 100 nautical miles north of the peninsula Yucatan the 9,000 HP diesel engine failed as a consequence of fatigue failure of the crankshaft. The ship was disabled and had to be towed to Veracruz, Mexico. The Swedish shipowning company decided to perform a temporary repair in Veracruz by welding the fatigue crack. Towing the motor vessel back to Sweden would have been too expensive.
Back in Sweden the damaged but repaired crankshaft was dismounted from the engine and inspected by surveyors. The result was that a fatigue crack had initiated from a subsurface solidification (hot) crack. The latter was formed during the solidification of the casting process. Before delivering the casted crankshaft to the engine manufacturer this crack was repaired by a so called 'weld for fabrication', which is a common procedure for large casted components. Unfortunately the repair weld was not appropriate in such a manner that the hot crack was only welded on its surface for a depth of 10 mm, the entire crack depth however was about 30 mm.
The shipowning company evaluated its amount of financial loss to 266,000 USD and filed a complaint at the German regional court in Düsseldorf against the German engine's manufacturer. The defendant contradicted the thesis of the Swedish surveyor, and the court of law entrusted (Federal Institute for Material's Research an Testing, a non commercial sovereign institute) BAM to carry out an independent survey report.
BAM survey report, predominantly based on metallographic analyses, stated the Swedish conclusions as applicable and moreover confirmed the results of the fracture mechanics based crack propagation calculations which are explaining a very slow crack propagation and a fast final failure even after more than 10<sup
>8 load cycles.
The lifetime reduction of cyclically loaded AISI 420C (X46Cr13, 1.4034) constantly exposed to highly corrosive CO2-saturated hot thermal water is demonstrated in in situ-laboratory experiments (60 °C, brine: Stuttgart Aquifer, flowing CO2: 30 L/h). SN plots, micrographic-, phase-, fractographic- and surface analysis were applied to obtain sustainable information on the corrosion and corrosion fatigue behavior. Maximum number of cycles (here 12.5 × 106 cycles to failure) is reached at σa = 173 MPa. Hydroxide and siderite layers were found on pits and crack surfaces. No typical fatigue limit exists and pit corrosion prior to crack initiation may be identified as failure cause.